Shutter actuating device

Abstract

A shutter actuating device of the type employing a piezoelectric element as an actuating element which attains stabilization of the shutter opening speed of a shutter device. The device includes a piezoelectric element charging circuit which charges a piezoelectric element with constant current so that the rising speed of the charged voltage of the piezoelectric element may be maintained constant. Means is also disclosed for minimizing a time lag until a minimum aperture for exposure is reached after triggering of a shutter release operation. Higher constant charging current is supplied to the piezoelectric element until a time just before the minimum aperture for exposure is presented, and after then the piezoelectric element is charged with lower constant current.

What is claimed is: 
     
       1. A shutter actuating device, comprising: a power source;   a boosting circuit for boosting a voltage of said power source;   a charging capacitor for accumulating therein a charge of electric energy boosted by said boosting circuit;   a shutter mechanism;   a piezoelectric element for actuating said shutter mechanism;   a first piezoelectric element driving means for charging said piezoelectric element with constant current by the electric energy accumulated in said charging capacitor so as to deform said piezoelectric element to operate said shutter mechanism to open the shutter;   a second piezoelectric element driving means for deforming said piezoelectric element in the opposite direction to close the shutter; and   an exposure controlling means for controlling said first piezoelectric element driving means to supply constant current to said piezoelectric element until an appropriate exposure amount is reached in accordance with a brightness of an object and a sensitivity of a film used and for controlling said second piezoelectric element driving means to deform said piezoelectric element in the opposite direction after the appropriate exposure amount has been reached.   
     
     
       2. A shutter actuating device as claimed in claim 1, wherein said first piezoelectric element driving means includes means for adjusting the constant current to a desired level. 
     
     
       3. A shutter actuating device as claimed in claim 2, wherein said first piezoelectric element driving means includes a circuit which is connected in parallel with said charging capacitor and includes the constant current circuit and a variable resistor connected in series to said piezoelectric element, said means for adjusting being constituted from said output stage of the constant current and said variable resistor. 
     
     
       4. A shutter actuating device as claimed in claim 3, wherein an output stage of the constant current circuit includes a transistor, said variable resistor being connected to the emitter of said transistor. 
     
     
       5. A shutter actuating device as claimed in claim 4, wherein said second piezoelectric element driving means acts to short-circuit said piezoelectric element. 
     
     
       6. A shutter actuating device as claimed in claim 5, wherein said exposure controlling means includes means for delivering a shutter position signal pulse corresponding to an aperture amount of the shutter, means for counting such pulses, and means for calculating a quantity of pulses indicative of an aperture amount by which an appropriate exposure amount can be attained in accordance with a brightness of an object and a film sensitivity, for comparing, after starting of an exposing operation, the calculated pulse quantity and the counted pulse quantity with each other, and for operating said second piezoelectric driving means when the calculated pulse quantity and the counted pulse quantity coincide with each other. 
     
     
       7. A shutter actuating device as claimed in claim 6, wherein said boosting circuit is a boosting circuit which is provided for driving a flash device, and said charging capacitor is a capacitor which is provided for driving said flash device. 
     
     
       8. A shutter actuating device, comprising: a power source;   a boosting circuit for boosting a voltage of said power source;   a charging capacitor for accumulating therein a charge of electric energy boosted by said boosting circuit;   a shutter mechanism;   a piezoelectric element for actuating said shutter mechansism;   a first piezoelectric element driving means for charging said piezoelectric element by the electric energy accumulated in said charging capacitor so as to deform said piezoelectric element to operate said shutter mechanism to open the shutter;   a second piezoelectric element driving means for deforming said piezoelectric element in the opposite direction to close the shutter;   a manually operable means manually operable to trigger an exposing operation;   a timing controlling means operable in response to operation of said manually operable means for controlling said first piezoelectric element driving means to supply first current to said piezoelectric element for a predetermined period of time before an exposing operation actually begins and then to supply, after lapse of the predetermined period of time, second current lower than said first current to said piezoelectric element; and   an exposure controlling means for controlling said first piezoelectric element driving means to supply current to said piezoelectric element until an appropriate exposure amount is reached in accordance with a brightness of an object and a sensitivity of a film used and for controlling said second piezoelectric element driving means to deform said piezoelectric element in the opposite direction after the appropriate exposure amount has been reached.   
     
     
       9. A shutter actuating device as claimed in claim 8, wherein said first piezoelectric element driving means includes a first charging means for supplying constant current to said piezoelectric element, and a second charging means connected in parallel with said first charging means, said timing controlling means causing both of said first and second charging means to be driven in response to operation of said manually operable means whereafter said timing controlling means causes only said second charging means to be stopped after lapse of the predetermined period of time. 
     
     
       10. A shutter actuating device as claimed in claim 8, wherein said first piezoelectric element driving means includes a charging means for supplying constant current to said piezoelectric element, a current controlling means connected to a current path of said charging means, and a bypass means connected in parallel with said current controlling means, said timing controlling means causing both of said charing means and said bypass means to be driven in response to operation of said manually operable means whereafter said timing controlling means causes only said bypass means to be stopped after lapse of the predetermined period of time. 
     
     
       11. A shutter actuating device as claimed in claim 10, wherein said current controlling means includes a variable resistor.